For a converter, just download Calibre. It will do all of them except DOC for me.

Epub tends to get the largest number of downloads.  It tends to be universal to most readers except for ones like Kindle which are proprietary formats.

I can tell you which is the one you don't want format wise:  PDF.  It is a fixed font and does NOT convert properly.  If it does when you try it count yourself lucky.

AZW and AZW3 are locked into Kindle alone.  No other ereader can read them and Calibre needs to convert them before it can display them.  It's a real pain.

On the other hand,  a Nook or my ereader or Kobo can read an epub.

How do I give you that + point you deserve?

click on the thankyou button on the top right of the post In case you didn't know, GIVING thanks improves your ranking too!

I'll add a couple of comments here too... even though I read with a Kindle (which used Mobi format) I prefer to get my books in ePub format because it seems to be the best file to convert FROM. I purchase books from Amazon for my Kindle and convert to ePub, but any other file I prefer ePub first.

I use Calibre to organize my entire eBook library. It's a great program, and only asks for donations by users that like the program. Besides converting eBook files to any other type, I prefer it because I can view and sort titles, change titles (for example, I always add Series info to the title so I can find it easier on my ereader), and review summaries of books before I read them. I also keep info in Calibre on books I've already read so I don't read them again!

HTH

ohk
What is the proprietary format?

That depends on what eReader you like to use?  If you are a Kindle user then it would have to be the .mobi and amazon's .azn format.  If you use the like of Kobo, Nook or Sony readers or any other android based type eReader software then the .epub format would be the best for those.  Most eReaders can read .pdf files without any problem.  But reading a .pdf file on a screen smaller than 7 inches is not recommended especially if you are using a eReader with an eInk screen.

Of course I do. How do you think I finished ADWD during 2nd term exams?